In the paper making industry, opacity, brightness and strength of the paper are desirable traits which are often balanced against each other. Opacity, the degree which the paper transmits light is particularly desirable for many applications; papers with a low opacity are difficult to read when images are printed on both sides. Many conventional opacifiers add excessive bulk to the paper thereby increasing the weight and the thickness of the paper.
It would be desirable to have a bright, opaque paper which is not excessively bulky and does not suffer a decrease in strength.
The present invention provides a novel method of opacifying paper, and a novel opacifier and opacifying composition which opacify as well as brighten paper. The novel opacifier comprises a mixture of at least one diglyceride and at least one amino-ester compound. Preferably the opacifier comprises from 17% to 72%, more preferably from 31% to 63%, most preferably from 45% to 55% diglyceride and preferably from 28% to 83%, more preferably from 37% to 59%, most preferably from 45% to 55% of the amino-ester compound.
The opacifying composition comprises: preferably from 0.1% to 100%, more preferably from 0.1% to 35%, even more preferably from 1% to 25%, most preferably from 7% to 15% of solids and preferably from 0 to 99.9999%, more preferably from 0.0001% to 99.9999%, even more preferably from 65% to 99.9%, even more preferably from 99% to 75%, most preferably from 85% to 93% of liquid, preferably water.
The solids comprise opacifier and surfactant. Preferably the solids comprise from 50 to 100%, more preferably from 80% to 99.9999%, even more preferably from 95% to 99.9998%, most preferably from 97% to 99.9%, opacifier; and preferably from 0% to 50% more preferably from 0.0001% to 50%, even more preferably from 0.0001% to 20%, even more preferably from 0.0022% to 5%, most preferably from 0.1% to 3%, surfactant. Preferably, the opacifying composition is an emulsion of the solids in water.
The inventions also relate to paper, methods of enhancing optical properties of paper and to methods of making the novel opacifying compositions.
The present invention provides a novel method of opacifying paper, and a novel opacifier and opacifying composition which opacify as well as brighten paper. The novel opacifier comprises a mixture of at least one diglyceride and at least one amino-ester compound. Preferably the opacifier comprises from 17% to 72%, more preferably from 31% to 63%, most preferably from 45% to 55% diglyceride and preferably from 28% to 83%, more preferably from 37% to 59%, most preferably from 45% to 55% of the amino-ester compound. The opacifying composition comprises the opacifier and preferably water.
The opacifying composition comprises: preferably from 0.1% to 100%, more preferably from 0.1% to 35%, even more preferably from 1% to 25%, most preferably from 7% to 15% of solids; and preferably from 0 to 99.9%, more preferably from 0.0001% to 99.9999%, even more preferably from 65% to 99.9%, even more preferably from 99% to 75%, most preferably from 85% to 93% of liquid, preferably water.
The solids comprise opacifier and surfactant. Preferably the solids comprise from 50% to 100%, more preferably from 80% to 99.9999%, even more preferably from 95% to 99.9998%, most preferably from 97% to 99.9%, opacifier; and preferably from 0% to 50%, more preferably from 0.0001% to 50%, even more preferably from 0.0001% to 20%, even more preferably from 0.0022% to 5%, most preferably from 0.1% to 3%, surfactant. All percentages are by weight unless otherwise stated.
Preferably, the opacifying composition is an emulsion of the solids in water.
An acid is preferably present in an effective amount to provide the opacifying composition with a pH less than 6. The acid is preferably present in an effective amount to provide the opacifying composition with a pH of from 3 to 6, more preferably 4 to 5.
The Opacifier
The opacifier comprises a mixture of at least one diglyceride and at least one amino-ester compound. The diglyceride has the following structure: 
wherein:
R1 is an alkyl group, preferably having from 4 to 23 carbon atoms, more preferably from 8 to 20 carbon atoms, most preferably from 10 to 17 carbon atoms;
R2 is an alkyl group, preferably having from 4 to 23, more preferably from 8 to 20 carbon atoms, most preferably from 10 to 17 carbon atoms;
wherein R1 and R2 are the same or different.
Preferably the diglyceride is a mixture having from 10% to 95%, more preferably from 51% to 90% diglyceride wherein R1 and R2 have 17 carbon atoms, and from 5% to 90%, more preferably from 10% to 49%, diglyceride wherein R1 and R2 have 15 carbon atoms.
Good results have been obtained using hydrogenated tallow, which has a mixture of diglycerides, comprising for example: 3.4% of a diglyceride where R1 and R2 have 13 carbon atoms; 28.9% of a diglyceride where R1 and R2 have 15 carbon atoms; 0.8% of a diglyceride where R1 and R2 have 16 carbon atoms; and 66.9% of a diglyceride where R1 and R2 have 17 carbon atoms.
Good results have also been obtained using soybean oil, which has a mixture of diglycerides comprising for example: 0.1% of a diglyceride where R1 and R2 have 13 carbon atoms and no double bond; 0.1% of a diglyceride where R1 and R2 have 13 carbon atoms and one double bond; 10.5% of a diglyceride where R1 and R2 have 15 carbon atoms and no double bond; 3.2% of a diglyceride where R1 and R2 have 17 carbon atoms and no double bond; 22.3% of a diglyceride where R1 and R2 have 17 carbon atoms and one double bond; 54.5% of a diglyceride where R1 and R2 have 17 carbon atoms and two double bonds; 8.3% of a diglyceride where R1 and R2 have 17 carbon atoms and three double bonds; 0.2% of diglyceride where R1 and R2 have 19 carbon atoms and no double bond; 0.9% of a diglyceride where R1 and R2 have 19 carbon atoms and one double bond.
The amino-ester compound has the following structure: 
wherein:
R4 is an alkyl group of from 4 to 23 carbon atoms, preferably from 10 to 17 carbon atoms;
R5 is an alkyl alcohol group of from 1 to 15 carbon atoms, preferably from 1 to 6 carbon atoms;
R6 is an alkyl group of from 1 to 15 carbon atoms, preferably from 1 to 6 carbon atoms, or an alkyl alcohol group of from 1 to 15 carbon atoms, preferably from 1 to 6 carbon atoms, or a hydrogen; and
R7 is an alkyl group of from 1 to 15 carbon atoms, preferably from 1 to 6 carbon atoms, or an alkyl alcohol group of from 1 to 15 carbon atoms, preferably from 1 to 6 carbon atoms, or a hydrogen;
wherein R5, R6, and R7 are the same or different.
Good results have been obtained wherein R5, R6, and R7 have two carbon atoms and R6, and R7 are alkyl alcohols.
Mixtures of diglycerides and mixtures of amino-ester compounds are also useful.
The Opacifying Composition
The opacifying composition comprises the opacifier, preferably a liquid the liquid preferably being water, preferably a surfactant, and preferably an acid. Preferably the surfactant is an ethylene oxide surfactant, preferably an ethoxylated tallow amine. Examples of other suitable surfactants are fatty acids ethoxylates, such as stearic acid with 20 moles of ethoxylate, fatty amine surfactants such as tallow amine with 15 moles ethoxylate, nonyl phenol ethoxylates, and fatty alcohol ethoxylates such as lauryl alcohol with 7 moles ethoxylate and stearyl alcohol with 24 moles of ethoxylate. Preferred acids are for example, acetic acid, propanoic acid, butanoic acid, pentanoic acid or methyl sulfate.
The salt is optionally added to reduce viscosity. Suitable salts are calcium chloride, sodium acetate and sodium bicarbonate. Preferably, the salt is present from 0.0022% to 1%, more preferably from 0.01% to 0.5%, most preferably from 0.1% to 0.3%.
Optionally, conventional antifoaming agents, bactericide, and fungicides are added to the opacifying composition or the opacifier or both.
Preparation of the Opacifying Composition
The opacifying composition is prepared by first combining a mixture comprising from 50% to 99%, preferably from 70% to 90%, more preferably from 76% to 86% by weight of at least one triglyceride, from 1% to 50%, preferably from 10% to 30%, more preferably from 13% to 23%, of an alkanolamine. Optionally a catalyst is present in an amount effective to catalyze the transesterification reaction. Preferably the catalyst is present from 0 to 5%, more preferably from 0.1% to 0.5%, more preferably from 0.075% to 0.15%.
The triglycerides are also known in the art as triacylglycerols. Sources for triglycerides are for example, tallow, soybean oil, castor oil, cottonseed oil, butter fat, and lard. The triglycerides have three alkyl groups each alkyl group having preferably from 4 to 23 carbon atoms. The triglyceride has the following structure: 
wherein:
R1 is an alkyl group having from 4 to 23 carbon atoms, preferably 8 to 20 carbon atoms, more preferably 10 to 17 carbon atoms;
R2 is an alkyl group having from 4 to 23, preferably 8 to 20 carbon atoms, more preferably 10 to 17 carbon atoms;
R3 is an alkyl group having from 4 to 23, preferably 8 to 20 carbon atoms, more preferably 10 to 17 carbon atoms;
wherein R1 R2 and R3 are the same or different.
The alkanolamine has the following structure: 
wherein:
R5 is an alkyl alcohol group of from 1 to 15 carbon atoms, preferably from 1 to 6 carbon atoms;
R6 is an alkyl alcohol group of from 1 to 15 carbon atoms, preferably from 1 to 6 carbon atoms;
R7 is an alkyl alcohol group of from 1 to 15 carbon atoms, preferably from 1 to 6 carbon atoms or an alkyl group of from 1 to 15 carbon atoms, preferably from 1 to 6 carbon atoms, or a hydrogen; and
wherein R4, R5 and R6 are the same or different.
Suitable alkanolamines are for example, diethanolamine, Nxe2x80x2, Nxe2x80x2, dimethylethanolamine and triethanolamine. Mixtures of triglycerides and mixtures of alkanolamines are also useful.
The mixture is then reacted, preferably under heat, to form the opacifying composition. Good results have been obtained by heating at 180xc2x0 C. to 200xc2x0 C. for one to two hours. The emulsion is formed by adding the opacifying composition to water which contains an acid, and a surfactant, and heating with agitation. Good results have been obtained by heating to 93xc2x0 C. for 30 minutes, then cooling to 70xc2x0 C., adding the salt and then cooling to room temperature.
In the emulsion of the opacifying composition, the amino-ester compound is present as an amine salt. The opacifying composition preferably contains less than 20% triglycerides, less than 10% monoglycerides, less than 4% free alkanolamine and less than 6% free glycerin.
The opacifying composition is added to a pulp slurry also known in the art as a xe2x80x9cfurnishxe2x80x9d, which then is used to form the 5 paper. The pulp slurry is made using conventional techniques.
The opacifying composition is added from preferably 0.1 to 15 pounds/ton, preferably 0.5 to 12 pounds/ton, more preferably 1 to 10 pounds/ton, most preferably 2 to 4 pounds/ton of pulp slurry.
After the slurry is formed it is stored in holding tanks or fed into a papermaking machine. The opacifying composition is added to the pulp slurry after the pulp has been bleached but before the pulp enters the head box of the paper making machine. The opacifying composition may be added to the slurry when it is in the holding tank or may be added to the slurry as it moves along to the headbox of the papermaking machine.
The paper made from the pulp slurry containing the opacifying composition is also made using conventional techniques.
The Paper
As used herein, xe2x80x9cpaperxe2x80x9d means a matted or felted sheet of fiber. Preferably the fiber is cellulosic. The paper of the present invention which is opacified with the opacifying composition comprises: fibers; at least one diglyceride; and at least one amino- ester compound. As used, herein xe2x80x9cpaperxe2x80x9d means all types of sheets containing cellulosic fiber and includes but is not limited to, tissue, toweling, cardboard, newsprint, fine paper, lightweight coated paper, bible grade, phone book grade, super calendar grade, liner board, reply card grade, cylinder board, and filled sheets. The amount of opacifier present on the paper is preferably from 0.0001% to 10%; more preferably from 0.01% to 5%, most preferably from 0.05% to 2%.